Optical interruption sensors, or “photo-interrupters”, are well known in the art and normally provide an opposed light transmitter, typically a light emitting diode (“LED”), and a light receiver (typically a phototransistor). The light transmitter and receiver may be placed in opposition as supported within a housing. The housing provides windows to permit a beam of light to pass from the light transmitter across a slot to the light receiver.
A light blocking vane, for example, a spoke on a rotating wheel or the like, may move into and out of the slot to block or permit passage of the light beam. In this way, detection of the light beam at the light receiver can be used to detect relative movement of the vane with respect to the housing. When the vane is on a rotating wheel, for example, interruption of the light beam detected at the light receiver provides an indication of rotational speed of the wheel.
The optical-interrupter may include an internal biasing circuit for controlling the brightness of the light transmitter and a detector circuit providing an electrical output (typically a binary signal) indicating whether the light beam is blocked or unblocked based on a pre-established threshold applied to an electrical signal from the light receiver.